Abstract The ultimate goal of Project 3 is to provide a firm basis for predicting exposure conditions in the human under which these materials could elicit effects in the maternal, fetal, or neonatal cardiovascular system. The research approach for this project is based on the hypothesis that an appropriate physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model for the disposition and effects ofthe engineered nanoparticles (ENMs) in one species can be used to provide quantitative predictions for another species, including the human. In this case, a PBPK/PD model will be developed using rat data from Projects 1 and 2, and the predictive power ofthe model will be tested using mouse data from Project 2. By incorporating human biology and data from human cells from Project 1, the model will provide a capability for quantitative extrapolation ofthe results of animal experiments to characterize the potential for human toxicity. The development ofthe PBPK model for nanoparticles will be conducted in a rigorous, step-wise manner, beginning with modeling ofthe processes associated with cellular uptake, localization, and clearance of nanoparticles using the in vitro data collected during Project 1 for epithelial and endothelial cells (Specific Aim 1). In Specific Aim 2, the cellular dosimetry model will be embedded in a PBPK description of the physiological time-course for gestation and lactation. The in vivo disposition data collected during Project 2 will be used to identify the whole-body PK parameters for the models. We posit that the cellular dosimetry model developed from in vitro data will accurately describe cellular dosimetry in the in vivo situation as well. We will test this hypothesis using in vivo tissue disposition data from Project 2. A similar step-wise approach will be used for the development of PD models of the various direct and indirect tissue responses to nanoparticle exposure in Specific Aim 3. The PD models will be designed to test two alternative hypotheses regarding cardiovascular toxicity of nanomaterials: either 1) direct induction of inflammatory responses and toxicity in target cells by the nanoparticles themselves, or 2) an indirect effect on vascular endothelial cells mediated by circulating cytokines produced in response to nanoparticle exposure in the portal of entry (e.g., alveolar epithelial cells). We hypothesize that both of these mechanisms contribute to the toxic effects of nanoparticles in different target tissues. The first 2 years of the project will focus on the development of the PBPK/PD model for the rat to provide a consistent description ofthe disposition and cardiovascular effects ofthe nanomaterials across multiple routes of exposure (i.e., intravenous [i.v.], oral, and inspirafion) and life stages (i.e., non-pregnant adult, pregnant dam and fetus, lactafing dam and pup). Comparison of target tissue dosimetry across these experimental condifions will allow evaluation ofthe relafive contribution ofthe direct and indirect mechanisms of toxicity and identification of susceptible life stages. In Years 3 through 5, PBPK/PD model parameterizations for the mouse and human will be developed (Specific Aim 4). In addition, our model structures will provide tools for Principal Investigators (Pis) in other centers to evaluate the potential systemic distribution and toxicity of other nanoparticles.